Peculiarities of TiH2 decomposition

Abstract

The eventual competition between the dehydrogenation and oxidation of TiH2 powder in the argon, oxygen, and static air atmospheres has been examined in the regime of linear heating using differential thermal analysis (DTA), X-ray diffraction, transmission and scanning electron microscopy coupled to energy dispersive spectroscopy techniques. Three stages of dehydrogenation, R1, R2, and R3, and two different oxidation reactions, O1 and O2, have been identified. The kinetics of individual reactions has been investigated by the Kissinger and Surinach curve fitting procedures. While the kinetics of O1, O2, and R1 reactions depends on the diffusivities of the external reagent gas, being oxygen, and internal product gas, being hydrogen, the main dehydrogenation stage R2 is controlled by the combined nucleation-and-growth and coalescence kinetics. The effect of pre-annealing of TiH2 on its subsequent degradation has also been studied. Due to the huge overheating accompanying both oxidation reactions in the DTA set-up, substantial thermal losses have been demonstrated and the method to obtain the true heat of oxidation reactions in metals has been described.